The present invention relates to a color filter substrate and a color electrooptical device, more particularly, to a method of manufacturing a color filter substrate and a color electrooptical device such as, for example, a color liquid crystal display device having a transparent electrode over a color filter formed on a transparent substrate.
FIG. 3 is a section showing a color liquid crystal display device of the prior art. Reference numeral 21 designates a substrate made of glass, numeral 22 a transparent electrode made of an indium-tin oxide (as will be referred to as "ITO"), and numeral 23 a color filter made of an organic polymer and a coloring material and prepared by dyeing, printing, electrodeposition or the like. The dyeing method and the printing method can dispense with the ITO of the electrode 22. Numeral 24 designates a second transparent electrode which is made of an ITO and formed to have its pattern registered with the color filter. This second transparent electrode 24 is prepared in the prior art by a sputtering method. Numeral 25 designates an opposed substrate which is formed thereover with a transparent electrode 26 of an ITO. The opposed substrate 25 is opposed to the substrate 21 to sandwich a liquid crystal 27 therebetween to constitute a multi-color liquid crystal display device. This liquid crystal display device can use the transparent electrode 24 over the color filter as a driving electrode for applying a voltage to the liquid crystal so that it can be freed from the voltage loss, which has been caused heretofore by applying the voltage through the color filter, and can apply the driving voltage directly to the liquid crystal. Thus, the liquid crystal display device has high practical values because it is suited for a drive at a low voltage.
If, however, the transparent electrode over the color filter is formed by the sputtering method of the prior art, the substrate temperature at the filming time cannot be raised to a high level due to the heat resistance because the color filter is made of an organic polymer. Thus, the process has to be accomplished at a lower temperature than that for filming over an inorganic substrate of glass or the like to deteriorate the contacting property between the formed film and the substrate. Moreover, it frequently occurs that the resistivity of the film does not drop. As a result, a defect such as separation is liable to occur, and a sufficiently low resistance cannot be obtained with a desired film thickness.
Generally, an organic polymer and an inorganic substrate such as the ITO are highly different in thermal deformation so that a displacement will easily occur at their interface when heated, if they contact merely in face-to-face relation. In the film formed by the sputtering method, the energy owned by particles reaching the color filter is relatively low so that the bond between the particles composing the film and the color filter is too weak to overcome the thermal stress at the interface. Thus, the defect such as separation, crack or the like seems to occur.
If, on the other hand, the organic polymer used is heated and filmed up to the limit of heat resistance so as to improve the contacting property, then the stress due to the thermal deformation of the color filter is easily concentrated at the film interface to cause a defect such as crack. In order to avoid this defect, an overcoat layer having a buffering action may be sandwiched between the color filter and the transparent electrode. However, it is considerably difficult for the steps, after the transparent electrode has been filmed, to satisfy the resistance to the heating treatment and the reliability at the time of an actual use. In order to improve the contacting property with the organic polymer, on the other hand, the transparent electrode is formed by an ion plating method, in which evaporation particles are ionized to make a film by a plasma beam, as disclosed in Japanese Patent Laid-Open No. 198419/1990.
This ion plating method is a means for remarkably improving the contacting property of the color film or the like to the organic polymer, but is difficult for the covering characteristics to reduce the resistivity and to provide a thin film transparent electrode having a low resistance.